Surgical catheters have long been used for a wide variety of surgical procedures. To this end, the catheter or catheter assembly is often times uniquely designed to satisfy the needs of a particular application (e.g., diameter, number of lumens, steering capabilities, provision of electrodes, etc.). The catheter material itself must be made from a biocompatible, thermoplastic material having requisite strength and flexibility. Universally accepted materials include nylon, polyethylene, polyurethane, Pebax®, etc. (hereinafter referred to as “standard catheter material” or “thermoplastic tubing”). In addition to being biocompatible and sufficiently flexible, each of these materials is characterized as being fluid impermeable. With this construction, fluid is readily distributed to a distal end of the catheter body from a fluid source located at a proximal end thereof.
The above-described fluid impermeable catheter materials are universally employed. More recently, however, a need has been recognized for dispensing or irrigating fluid along a sectional length of the catheter body. For example, certain medical treatments require destruction of internal tissue through ablation. Typically, tissue ablation (such as heart tissue for treatment of atrial fibrillation) entails delivering an electrode, or series of electrodes, to the target site. The ablating electrode(s) is normally delivered via a catheter. Regardless, electrical energy, such as RF energy, is applied to the contacted tissue by the electrode(s) thereby achieving the desired ablation. For certain procedures, an enlarged or elongated ablation lesion pattern is desired. With available ablation electrode catheters, however, difficulties in properly positioning the electrode(s), achieving the desired level of ablation, etc., may be experienced. These potential complications can be avoided by forming a “virtual electrode” along a section of the delivering catheter. More particularly, the catheter includes an ablation section formed of a microporous material. A conductive fluid, such as saline, is forced into a lumen of the catheter and is then irrigated outwardly through the microporous ablation section. RF energy is applied to the irrigated fluid, thereby forming the virtual electrode that otherwise performs the desired ablation. Examples of catheter assemblies effectuating this technique for treatment of atrial fibrillation are provided in U.S. patent application Ser. No. 09/848,555, filed on May 3, 2001 and entitled “Ablation Catheter Assembly with Radially Decreasing Helical and Method of Use”, the teachings of which are incorporated herein by reference.
For tissue ablation, as well as other procedures in which liquid is irrigated along a catheter section, it is typically important that a substantially uniform fluid distribution be achieved. To this end, high density, expanded polytetrafluoroethylene (“ePTFE”) has been identified as uniquely satisfying the desired surgical irrigation characteristics. ePTFE material is readily formable as a tube, provides a pore size on the order of 5–25 microns and is highly flexible. ePTFE tubing appears highly viable for catheter irrigation applications.
Due to the relatively high cost of ePTFE, it is not cost effective to form an entire catheter from ePTFE material when only a small segment is required for the irrigation application. Instead, a catheter assembly including ePTFE material must entail a desired length of ePTFE tubing secured to a length of standard thermoplastic catheter tubing. The resulting assembly is relatively inexpensive, biocompatible, and flexible, with fluid only being distributed along the section of ePTFE tubing. Unfortunately, ePTFE does not liquefy or otherwise bond in a manner otherwise found with standard thermoplastic catheter materials. That is to say, the accepted catheter bonding technique of forming a re-flow butt joint will not work, as the ePTFE will not liquefy when heated. Further, there are only a limited number of available adhesives that will bond to ePTFE material, such that construction of an appropriate catheter using only an adhesive is quite difficult. Along these same lines, the available adhesives cannot consistently provide a sealed bond between ePTFE material and standard thermoplastic catheter materials, resulting in less than optimal results.
The recent development of ePTFE material and the subsequent recognition of its usefulness as part of a medical catheter design provides a distinct advancement in the catheter art. Unfortunately, bonding of ePTFE tubing to standard thermoplastic catheter tubing cannot be satisfactorily achieved with known techniques. Therefore, a need exists for a method of forming a medical catheter including a section of ePTFE tubing coupled to a length of standard catheter tubing.